Synthesis of esters of lower aliphatic alcohols



United States Patent SYNTHESIS or ESTERS 0F LOWER ALIPHATIC ALCOHOLSLawrence G. Hess and Helmut W. Schulz, Charleston, W. Va., assiguors toUnion Carbide Corporation, a corporation of New York No Drawing.Application August '5, 1957 Serial No. 676,443

9 Claims. (Cl. 260-488)- wherein R represents a lower aliphatichydrocarbon radical composed of carbon, hydrogen and oxygen;

As is well known when carbon monoxide is reacted,

with an alcohol a variety of carbonylated products are producedincluding esters, acids, ethers and the like.

It has been discovered that when carbon monoxide and an alcohol arereactedat elevated temperatures and pressures in the presence of anickel or nickel carbonyl catalyst promoted with a minor amount ofhydrogen iodide there is produced a reaction mixture wherein thecarbonylated product is predominately the ester'of a lower aliphaticmonohydric alcohol.

Considerable work has been done in the field to which this inventionrelates, and, as a consequence, there are a number of patents andliterature publications outstanding which describe the reaction ofmethanol and carbon monoxide in the presence of various catalysts. Thereactionsdescribed in the prior art were principally liquid phaseprocesses and produced various products including, for example, aceticacid, methyl acetate and other oxygen containing products, all in lowproductivity. We have found that by employing our particular catalystsin an essentially vapor phase process we have been able to obtain highproductivity of the esters of lower aliphatic alcohols when carbonmonoxide and a monohydric lower aliphatic alcohol are reacted in thepresence of these catalysts under the reaction conditions provided bythis invention.

Heretofore, it has been known that methyl acetate, as well as othersimple esters in the case of the appropriate alcohol, can be prepared bythe reaction of carbon monoxide and methanol in the presence of certaincatalysts, such as, for example, the ferrites, ferrates, cobaltites andcobaltates of the alkali and alkaline earth metals, including sodium,potassium, bar

2,898,366 Patented Aug. 4, 1959 trifluoride and the like. Also, varioussilicotungstates, borates and phosphates have been used as catalysts forthe reaction. Nickel and cobalt halides have been mentioned assubstances which may be employed in combination with boron trifluoride,or activated carbon as catalysts for the reaction, according to theprior art.

In general, the aforementioned processes for the reaction of methanoland carbon monoxide were liquid phase processes and either involved theuse of highly corrosive catalysts, or gave rise to comparatively lowyields of the desired end products, such as, acetic acid, or methylacetate.

Therefore, it is an object of this invention to provide an improvedprocess for reacting alcohols with carbon monoxide to produce esters ofhigh molecular weight. Another object of this invention is to produceesters from an alcohol and carbon monoxide in high yield by theutilization of a catalyst which'is soluble in the alcohol therebyproviding an improvement in adapting the process to continuousoperation.

It is a further object of this invention to provide a novel process forthe production of esters of lower aliphatic alcohols to the substantialexclusion of other oxygenated products formed during the reaction. Astill further object of this invention is to provide a novel process forreacting carbon monoxide and a lower aliphatic monohydric alcohol toproduce a reaction mixture comprising essentially the carbonylatedproduct in the form of an ester of the particular lower aliphaticmonohydric alcohol.

It has been discovered that when a lower aliphatic monohydric alcohol,such as, methanol, and carbon monoxide are reacted together in thepresence of a catalyst comprising a nickel salt of analiphaticmonocarboxylic acid promoted with a minor amount of iodine orhydrogen iodide, we obtain an ester of the lower aliphatic acidcontaining one more carbon "atom than the monohydric alcohol in veryhigh yields. Additionally, when the catalysts of this invention areused, for example, in conjunction with carbon monoxide and methanol thereaction is directed preferentially to the formation of methyl acetaterather than acetic acid.

The nickel salts of aliphatic monocarboxylic acids suitable for use inthe process of this invention are nickel formate, nickel acetate andnickel propionate. The preferred salt is nickel acetate. a

The process of this invention is usually carried out at a temperaturenot substantially lower than 325 C. Essentially the reaction is a vaporphase reaction, since the preferred operating temperature range (325 C.to

400 C.) is above the critical temperatures of methanol,

pressures are generally employed while pressures ranging upwards of 3000p.s.i. are preferable. Most advantageous results are obtained whenoperating in a pressure range of from about 4000 p.s.i. to about 6000p.s.1.

One of the advantages derived from using the catalyst and promotercombinations is that the catalyst and promoter are soluble in thereactant methanol.

Catalyst concentrations are important in the practice of this inventiononly to the extent that enough catalyst should be present to promote thecarbonylation of the alcohol. Catalyst concentrations in the range ofabout 0.5% to about 2%, by weight, of the nickel salt of themonocarboxylic acid, based on the quantity of alcohol charged to thereaction, are usually suflicient to promote the reaction.

The amount of promoter is not necessarily critical but should be presentin an amount suflicient to activate the catalyst. A preferred range ofpromoter concentration is in the range of about 10% to about 50%, byweight,

based on the weight of catalyst charged to the reaction vessel.

In the practice of the invention the mol ratio of carbon monoxide tolower aliphatic monohydric alcohol is not to insure a complete purgingof the system. Reaction gas was then added up to the pressurescalculated from the gas law relationships to give the desired totalpressure at the approximate expected temperature of reaction.

necessarily critical and can be varied over a wide range. 5 Thecalculations were modified as suggested by the data It has been foundthat suitable conversions of alcohol to obtained in the course of theexperiments.

esters can be obtained when the rnol ratio of carbon Next, rocking andheating were initiated in a manner monoxide to alcohol is varied from aslow as 0.63:1 to which would result in minimum exposure to warm-up ashigh as 2.07:1. It is preferred however to operate period and yet wouldnot result in temperatures excesthe process of this invention whereinthe rnol ratio of sively above the desired operating temperature. Whencarbon monoxide to alcohol is maintained in the range of the reactionconditions had been maintained for the refrom 1:1 to about 1.5 :l.quired period of time, heating was discontinued and a Broadly stated,this invention is directed to a process stream of air was passed aroundthe reaction vessel (infor the production of organic oxygen-containingcomside the heater) to facilitate rapid cooling of the reaction pounds,which comprises reacting a saturated aliphatic s l nd its contents to pply This monohydric alcohol with carbon monoxide in the prescooling airwas also used to help control the exothermic ence of a catalyticquantity of a nickel salt of an aliphatic reactions. monocarboxylic acidpromoted with a minor amount of When low boiling components wereexpected in the a compound selected from the group consisting of iodinereaction product a blowdown procedure was used which and hydrogen iodideand separating, from the resulting involved chilling the reaction vesselin acetone-solid carreaction product, the organic oxygen-containingcombon dioxide slurry prior to bleeding the gas. The gas pounds producedby the reaction. More specifically, our was discharged through afifty-foot copper coil and cold invention is directed to a process forthe production of traps cooled with acetone-solid carbon dioxide slurry,methyl acetate, which comprises reacting methanol and then passedthrough a gas sample tube and measured carbon monoxide at an elevatedtemperature in the range 5 finally with a wet-test gas meter. If a glassliner was of 325 C. to 400 C. and at an elevated pressure in the used,separate weights were obtained on the material range of from about 4000p.s.i. to about6000 p.s.i. in recovered inside the liner and thematerial removed from the presence of a catalytic quantity of nickelacetate prothe bomb outside the liner, both portions being combinedmoted with a minor amount of a compound selected for distillation andanalysis. A complete analysis was from the group consisting of iodineand hydrogen iodide. obtained by fractional distillation, followed by achem- The carbonylation reaction may be carried out, either icalanalysis of the fractions, which permitted calculation continuously orby batch process, as desired. of the data presented in Table I.

Table I Temperature, C. P Efiieiencies (Percent) Run Catalyst andPromoter Weight, 8. 5 5 'i iii e tirit r fs i i,

percent b Maximum (Min.) percent Methyl Acetic Di- Imtial e MaximumTotal Acetate Acid methyl Ether 1 gggfg fi fggfia 347 390 5,000 15 67.783.7 67.1 12.5 4.1 2 NcimlAcmte-m 334 345 4,300 74.0 89.1 76.0 8.9 4.2323 340 4,100 15 79.4 86.7 58.9 0.0 18.2 5 352 350 4,500 15 78.9 71.750.0 12.7 5 {Hydrogen Iodide 350 362 4,700 30 61.6 83.8 77.1 4.7 2.0 6Nickel Acetate (No Pro- 1. 4 350 350 5, 400 15 10. 0 7 a l g: 320 5526,000 15 88.7 82.5 8 "{Hydmgen Iodide fig 342 345 5,000 50 01.2 68.8

Temperature at which the reaction was initiated. b Catalyst and promoterconcentrations based on alcohol charged. 6 Molar ratio of carbonmonoxide to methanol was 0.63:1.

d Molar ratio of carbon monoxide to methanol was 2.07:1.

The following Table I illustrates a series of batch ex- From anexamination of the data presented in Table I per ments defining theminimum reaction conditions it is interesting to note that when nickelacetate is used wh ch would afiord acceptable conversions andproducwithout a promoter (run 6), the conversion of methanol t1v1t1esfor the reactlon of methanol and carbon monoxide is low. Additionally,methyl acetate was produced as to form methyl acetate or acetic ac1d.the predominant product even though the ratio of carbon Thus, thestandard condltions for the experiments monoxide to methanol was variedover a wide range as illustrated 1n Table I were set at a temperature of350 C., illustrated by runs 7 and 8.

a system pressure of 4000 p.s.i. to 5500 p.s.i., an eifective Similarly,ethyl propionate was produced when a mixreactlon time of 15 to 30minutes, and a carbon monoxide ture of 313 grams of ethanol, 4.0 gramsof nickel acetate, to methanol molar ratio of 1.5 :1 except asindicated. and 2.1 grams of hydrogen iodide was reacted with car- Thecarbonylation of methanol was carried out in a bon monoxide in the sametype of equipment described rocker-type reaction vessel similar to thoseused in estababove for batchwise reactions of methanol and carbon lishedtechniques for laboratory hydrogenations. In monoxide. The reactionvessel and contents were heated some experlments, removable glass linerswere employed. under an initial carbon monoxide pressure of 1200 poundsAfter the reaction vessel had been charged with liquid per square inchto a temperature of 350 C. and mainand sol1d components, it was closedand placed in the tained at 350 to 360 C. and a pressure of 4200 poundsheating and rocklng mechanism, which was suitably fitted per square inchfor a period of ten minutes. Distilla- .w1th the necessary auxiliaryequipment. Carbon montion of the crude reaction product discharged fromthe oxide was introduced into the reaction vessel at approxicooledreaction vessel gave fractions which through chemimately 500 p.s.i. andexpelled from the vessel three times cal and mass spectrometric analysesdemonstrated yields of ethyl propionate' and propionic acid of 43.3 and6.9 percent, respectively, based on the ethanol charged to the reactionvessel.

Table H is presented below to illustrate the marked differences inconversions, yields, catalytic materials and operating conditionsbetween this invention and previous processes for the production ofmethyl acetate by the reaction of methanol and carbon monoxide.

alkanolswherein the ester formed contains one more carbon atom than thesum of the carbon atoms of two alkanol molecules in which a loweralkanol is reacted with carbon monoxide, the improvement which comprisescarrying out the reaction in the presence of a catalytic amount of anickel salt of a lower alkanoic acid pro moted with a minor amount of acompound selected from the group consisting of iodine and hydrogeniodide at a T able II Meth- Temperature, C. Pressure, Reaction MethanolMethyl Reference C11101, g ater, ozla talysttand Grams Mp.s.i.,w'llfimeta, Conrgar- @getfite I rams rams rOmo er axlmum mu e5 S1011BI'- 19 Initial Maximum cent Percent Example 1, Prior Art 12s asfffffff}: 12 220 225 11,600 a5 26. s 15. 6 Example 2, Prior Art e4 723,33 3} 220 220 10, 250 30 7.0 Example 3, Prior Art e4 72 {$222 f 5 220220 10,25o 30 25.0

Nickel Acetate 3. 5 Run 1, Table I 24s {g i g z t g g "347 396 5, 00067.7 45. 3

16 e Ce 3 9.--

Run 4, Table I 237 {Hydrogen 5 352 359 4, 500 15 78.9 46. 5

Yield based on methanol charged.

1:3 ratio of H2 to O0 in process gas.

*Iemperature is above critical temperature of reactants and products.

Table III, set forth below, reflects the high productivity of theprocess of our invention in terms of grams of product per hour per literof methanol charged to the reaction which is in sharp contrast to theknown process as illustrated in Table II, which utilizes from 6 to 8.5percent, by weight of a cobalt acetate catalyst and discloses, at best,an hourly conversion rate of methanol to methyl acetate of from 15 to 50percent.

B Corresponding to the runs of Table I. b Grams of product per hour perliter of methanol charged.

The procedure given below illustrates a suitable method of carrying outthis invention by a continuous process. The converter is a high-pressurereactor equipped with a Dowtherm jacket, the reactor being filled with acatalyst support similar to Alfrax or Aloxite. Methanol containing thenickel acetate catalyst and the promoter, hydrogen iodide, is fed to theconverter by means of a high-pressure liquid pump. Carbon monoxide under4500 pounds per square inch pressure is mixed with the methanol feed atthe entry to the reactor. The carbon monoxide and methanol pass throughthe reactor at 350 C. to 370 C. The reaction products pass out of thereactor through an expansion valve (pressure controller), where thepressure is reduced from 4500 pounds per square inch to 20 to pounds persquare inch, through a condenser, and into a liquid separator vessel,where the liquid products are collected, measured, and processedperiodically. The slight back pressure of 20 to 25 pounds per squareinch is beneficial in the condensation of the low boiling products. Theofi-gas from the liquid separator may be re-compressed and recycled tothe reactor.

This application is a continuation-in-p-art of application Serial No.384,774, filed October 7, 1953, now abandoned.

What is claimed is:

1. In a process for the production of esters of lower C. in the presenceof nickel acetate temperature in the range of from 325 C. to 400 C.under superatmospheric pressures in the range of from 3000 to 6000pounds per square inch absolute.

2. In a process for the production of esters of lower alkanols whereinthe ester formed contains one more carbon atom than the sum of thecarbon atoms of two alkanol molecules in which a lower alkanol isreacted with carbon monoxide, the improvement which comprises carryingout the reaction in the presence of nickel acetate promoted with a minoramount of hydrogen iodide at a temperature in the range of from 325 C.to 400 C. under superatmospheric pressures in the range of from 3000 to6000 pounds per square inch absolute.

3. In a process for the production of esters of lower alkanols whereinthe ester formed contains one more carbon atom that the sum of thecarbon atoms of two alkanol molecules wherein a lower alkanol is reactedwith carbon monoxide, the improvement which comprises carrying out thereaction in the presence of nickel acetate promoted with a minor amountof iodine at a temperature in the range of from 325 C. to 400 C. undersuperatmospheric pressures in the range of from 3000 to 6000 pounds persquare inch absolute.

4. A process for the production of esters of lower alkanols wherein theester formed contains one more carbon atom than the sum of the carbonatoms of two alkanol molecules which comprises reacting a lower alkanolwith carbon monoxide in the presence of a catalyst comprising a nickelsalt of a lower alkanoic acid promoted with a minor amount of a compoundselected from the group consisting of iodine and hydrogen iodide at atemperature in the range of from 325 C. to 400 C. under superatmosphericpressures in the range of from 3000 to 6000 pounds per square inchabsolute, and re covering the esters of said lower alkanols.

5. A process for the production of methyl acetate which comprisesreacting methanol and carbon monoxide under superatmospheric pressuresin the range of from 3000 to 6000 pounds per square inch absolute and ata temperature in the range of from 325 C. to 400 C. in the presence ofnickel acetate promoted with a minor amount of a compound selected fromthe group consisting of iodine and hydrogen iodide.

6. A process for the production of methyl acetate which comprisesreacting methanol and carbon monoxide under superatmospheric pressuresin the range of from 3000 to 6000 pounds per square inch absolute and ata temperature in the range of from 325 C. to 400 promoted with a minoramount of hydrogen iodide.

7. A process for the production of methyl acetate which comprisesreacting methanol and carbon monoxide under superatmospheric pressuresin the range of from 3000 to 6000 pounds per square inch absolute and ata temperature in the range of from 325 C. to 400 C. in the presence ofnickel acetate promoted with a minor amount of iodine.

8. A process for the production of esters of lower alkanols wherein theester formed contains one more carbon atom than the sum of the carbonatoms of two 211- kanol molecules which comprises reacting loweralkanols having dissolved therein a nickel salt of a lower alkanoic acidand a compound selected from the group consisting of iodine and hydrogeniodide with carbon monoxide at a temperature in the range of from 325 C.to 400 C. under superatmospheric pressures in the range of from 3000 to6000 pounds per square inch absolute and recovering the esters of saidlower alkanols.

9. A process for the production of esters of lower alkanols wherein theester formed contains one more carbon atom than the sum of the carbonatoms of two alkanol molecules which comprises reacting lower alkanolshaving dissolved therein a nickel salt of a lower alkanoic acid and acompound selected from the group consisting of iodine and hydrogeniodide with carbon monoxide in the vapor phase under superatmosphericpressures in the range of from 3000 to 6000 pounds per square inch ab-10 solute and recovering the esters of said lower alkanols.

References Cited in the file of this patent UNITED STATES PATENTSGlasebrook June 14, 1955 2,739,169 Hagemeyer Mar. 20, 1956

1. IN A PROCESS FOR THE PRODUCTION OF ESTERS OF LOWER ALKANOLS WHEREINTHE ESTER FORMED CONTAINS ONE MORE CARBON ATOM THAN THE SUM OF THECARBON ATOMS OF TWO ALKANOL MOLECULES IN WHICH A LOWER ALKANOL ISREACTED WITH CARBON MONOXIDE, THE IMPROVEMENT WHICH COMPRISES CARRYINGOUT THE REACTION IN THE PRESENCE OF A CATALYTIC AMOUNT OF A NICKEL SALTOF A LOWER ALKANOIC ACID PROMOTED WITH A MINOR AMOUNT OF A COMPOUNDSELECTED FROM THE GROUP CONSISTING OF IODINE AND HYDROGEN IODIDE AT ATEMPERATURE IN THE RANGE OF FROM 325*C. TO 400*C. UNDER SUPERATMOSPHERICPRESSURES IN THE RANGE OF FROM 3000 TO 6000 POUNDS PER SQUARE INCHABSOLUTE.